Microtome specimen holder



Sept. 8, 1953 H, KAHLER 2,651,236

MIGROTOME SPECIMEN HOLDER Fild Aug. 8, 1951 ATTORNEY Patented Sept. 8, 1953 UNITED STATES PATENT OFFICE (Granted under Title 35, U. S. Code (1952), sec. 266) Claims.

'Ihe invention described herein may be manufactured and used by or for the GovernmentI of the United States for governmental purposes without the payment to me of any royalty thereon in accordance with the provisions of the Act of April 30, 1928 (Ch. 460, 45 Stat. L. 467).

This invention relates to a microtome specimen holder and more particularly relates to a microtome holder which is capable of being advanced at a constant rate.

Electron microscropy of tissue sections and the like is successful only when the sections are of the order of 0.1 micron thick. It should be possible to study the three dimensional structure of tissue by preparing a series of sections of a given tissue, each section having a known and uniform thickness. Preparing such a series requires a microtome advancing mechanism that will satisfy rigorous conditions of constancy and reproducibility. It has been proposed to precool a specimen holder with carbon dioxide and to slice sections of tissue from the sample as the block warms to room temperature, the operator guessing at the time interval required to reproduce then a suitable thermal extension of the rod or block. Such a system is not considered generally satisfactory.

Accordingly, an object of this invention is to provide a microtome specimen holder which has a uniform rate of expansion to enable slices of tissue to be taken at known intervals of time to obtain uniform widths of the slices.

Another object of the invention is to provide a microtome specimen holder wherein the rate of expansion is reproducible.

An additional object of the invention is to provide a specimen holder for a thin slicing microtome where the specimen holder rod may be uniformly advanced to the position of the cutting knife, thereby permitting a series slices of the specimen to be cut, each slice of the order of 0.1 micron in thickness.

These objects are accomplished by this invention by utilizing a metallic rod which is wound with resistance wire insulated from the block and from the atmosphere and passing a current through the resistance wire which serves as a heating coil to cause advancement of the block due to thermal expansion of the metal. These objects will become apparent from a consideration of the accompanying drawing where Figure l is a cross section of the microtome specimen holder.

Figure 2 is a circuit diagram including the heating coil of the microtome specimen holder.

As shown in the drawing, the microtome specimen holder includes a block of metal IU. The block is formed of any metal which has a known, definite linear coeilcient of expansion. A definite length of linear expansion will be required to obtain a sequence of slices. A length of expansion of the order of three or four microns is satisfactory and, in fact, preferred. It is obvious that the length of the block will depend upon the particular metal used to obtain this length of expansion since the length of expansion is a function of the coefficient of expansion, the change in temperature and block.

A sleeve II of insulating material surrounds the block. Any electrical insulating material is suitable as long as there is no electrical contact between the block and the hereinafter described resistance wires. Mica is preferred as the insulating material for this sleeve.

Coiled around the block and insulated therefrom by the mica resistance wire I2. In this configuration the wireforms in effect a heating coil. ably connected to a source of electrical current which current may be varied in order to control the temperature of the wire, and hence of the block, to any desired degree as ticularly described hereinafter.

superimposed upon the wire coil I2 is a second sleeve of insulating material I3 with the same characteristics asinsulating sleeve II and again preferably formed of mica.

A sleeve I4 of thermal insulating material is` superimposed on sleeve I3. This thermal insulating sleeve, as the term implies, is used in order to concentrate the heat generated in the resistance coil I2 into the block IIJ rather than to allow this heat to be dissipated into the atmosphere.

A socket I5 is provided in one end of the block in order to allow for the mounting of the specimen block I6. Specimens to be held for cutting in the microtome are normally mounted in a block of plastic or the like. As shown in Figure l, the mounting socket I5 is provided with threads as is the plastic block I6 which holds the specimen. It is obvious that any suitable holding means used other than threads may be utilized as long as the specimen is rigidly and immovably mounted in the socket.

At the other end of the block, a collar I1 of suitable insulating material is provided. As is obvious from a consideration of the drawing, this collar insulates the block I 0 from the jaws I 8 the length of the sleeve I I is a length of high The wire is suit-` 3 of the microtome so that heat not dissipated to these jaws. As shown in the gure, set screw I9 in the jaws of the microtome will also be insulated from the block by collar` l1.

In order to read the temperature of the block I, particularly for device testing purposes, a thermo-couple -20 is lmounted in the block. Any suitable means such as insulating .collet 2| is used to provide an exit for the thermo-couple from the device.

As hereinbefore described, the resistance coil I2 is suitably connected to a source of electrical current as through leads 22 and 23,- zand switch 28 (normally closed), to a variable auto transformer 24 connected to step-'down transformer 25, in turn connected to the line terminals 26. A voltage is applied in order to obtain a constant heating of the block Ill due to theresistance of the wire coil I2. It will be appreciated that a substantially constant applied voltage will cause aA constant heating of the block iilandthev desired slices may be taken at the desiredinterv'als of time. In order to enable the-'operator torstop the expansion for a vshort time, if need arises, and then continue with the same cutting schedule, an additional resistor 21` maybe connected to the circuit. In. such cases the operator may throw the switch thereby placing the resistor in series in the circuit and hence preventing further heating of the block I0. It may be seen that such a circuit will alsoprevent the block from cooling and hence contracting.

One particular :embodiment of, the invention consists of a block l made of brass with dimensions of 2 inches in length and lae'inchesin diameter. The block sy wound with 20 feet of resistance wire having a resistance 'of' '78.1 ohms. The thus formed wire coil is 'electrically insulated from the block by a thin sheet of micail. 'The outer surface of the wire is .thermally insulated by a cylinder of methacrylate' 1%v inches long and 1/4 inchthick. 'The block isi-nsulated' from the jaws 18 of the microtome by a phenol-formaldehyde collar i1 whichis 1/8 inch thick. The power line available is connected to a transformer and a voltage output of volts is utilized. With'this-holder and a resistance'coil of "78 ohms, an applied voltage Iof 10 volts gives an-'eXpansion of the holder amounting to three microns lin six minutes.

It will' be appreciated fromy a reading of the foregoing speciiication that the invention-herein described is susceptible of various'vchanges and modications without departing'from the spirit and scope thereof. The invention is, therefore, tov be limited only by the scope and spirit asset forth in the appended claims.

What is claimed is:

1. A microtome specimen holder comprising a metallic block, a sleeve of insulating material around a portion of said block, a coil of resistance wire'surrounding said sleeve,.a'socket for mounting a specimen in one end of said block, a collar of insulating material at the other end of said block to insulate said block from the supporting jaws of the microtome and means for passing a current through said vcoil of resistance wire.

2. A microtome specimen holder comprising a from the block is metallic block, a sleeve o insulating material around a portion of said block, a coil of resistance wire surrounding said sleeve, a second sleeve of insulating material superimposed on said coil, a socket for mounting a specimen in one end of said block, a collar of insulating material at the other 'end of said block, said collar serving to insulate said block from the supporting jaws o the microtome and means for passing a current through said coil of resistance wire.

3. A microtome specimen holder comprising a lmetallic block, a sleeve of electrical insulating .material around a portion of said block, a coil of resistance wire surrounding said sleeve, a second sleeve ofA electrical insulating material superimposed lon said coil, a sleeve of thermal insulating material superimposed on said second sleeve of -xelectrical insulating material, a socket for mounting a specimen in lone end oi' said block, a collar of insulating material at the other end of said block, said collar servingto insulate said block fromfthe supporting jaws of the microtome, and means for passing a current through said coil of resistance w1re.

4. A microtome specimen Vholder comprising a metallic block, a sleeve of mica around a portion of said block, a coil of resistance wire surrounding said sleeve, a Second sleeve ofmica superimposedV on said coil, a sleeve of thermal insulating material superimposed on said second mica sleeve, a socket for mounting a specimeninone end of said block, a collar of. insulating material at the other end of said block, said collar-serving to ,insulate said block from said supportingjaws of rthe microtome, means for passinga current through said coil of resistance wire, and ,means for varying the amount .of current through said wire to thereby control the temperature of said block.

5. A microtome specimenholder comprising a metallic block, a sleeve of insulating material around a portion of said block, a coil 'of resistance wire surrounding said sleeve for heating said block, a socket for mounting a` specimen in one end of said. block, a collar of insulating material at the other end of said block to insulate said block from the supporting jaws of the microtome, circuit means connecting said heating coil toa source of electrical energy, means in said circuit to adjust the input to said coil to thereby cause said coil to heat and the temperature of said block to rise at a substantially constant rate, resistance means adapted to be connected inseries inl said circuit to thereby decreaseV the current to said heating coil and to Vthereby maintain the block at a Asubstantially constant temperature, and means for placing said resistance insaid series circuit and for removing it therefrom, thereby enabling the temperature increase of said block to be periodically interrupted without cooling said block.

HERBERT KAl-ILER.

References Cited in the file of this patent 

